Maura Pavan

CUORE: a cryogenic underground observatory for rare events

CUORE is a proposed tightly packed array of 1000 TeO2 bolometers, each being a cube 5cm on a side with a mass of 760g. The array consists of 25 vertical towers, arranged in a square of 5 towers×5 towers, each containing 10 layers of four crystals. The design of the detector is optimized for ultralow-background searches: for neutrinoless double-beta decay of 130Te (33.8% abundance), cold dark matter, solar axions, and rare nuclear decays. A preliminary experiment involving 20 crystals 3×3×6cm3 of 340g has been completed, and a single CUORE tower is being constructed as a smaller-scale experiment called CUORICINO. The expected performance and sensitivity, based on Monte Carlo simulations and extrapolations of present results, are reported.

A scintillating bolometer for experiments on double beta decay

Abstract The scintillation yields of CaF 2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first “scintillating bolometer” where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from α -particles in the energy region of interest for searches on double beta decay of 48 Ca can be achieved.

Methods for response stabilization in bolometers for rare decays

Abstract Massive bolometric detectors operated at very low temperatures (≃10xa0mK) can be used to search for rare events, such as Double Beta Decay and interactions of Dark Matter candidates. In experiments of this type it is important to keep the detector response steady within 0.1% level over periods of the order of one year or more, often in conflict with the intrinsic instabilities of the cryogenic setups. Here, a powerful method to stabilize detector response is described: using calibrated amounts of energy, injected by means of alpha particles or resistive heaters, a correlation between pulse amplitude and detector bias can be established. This correlation can be used to correct off-line the amplitudes of every pulse. The satisfactory results achieved with this technique are reported and discussed. For this purpose heavily doped Si heaters with steady resistances at cryogenic temperatures were designed and succesfully tested.

Measurements of internal radioactive contamination in samples of Roman lead to be used in experiments on rare events

Improved results of a series of measurements carried out on two diAerent types of Roman lead to be used in shields for experiments on rare events are reported. The chemical impurities in both samples have been determined by neutron activation. Underground measurements based on c-spectroscopy on large masses of the two types of lead, show the absence in both samples of radioactive contamination from 214 Bi and 232 Th, in secular equilibrium, with upper limits of a few tenths of a mBq kg ˇ1 . The contamination from 40 K is less than a few mBq kg ˇ1 . Much care has been addressed to the contamination due to 210 Pb which breaks secular equilibrium and which contributes to most of the background in experiments searching low energy events like direct interactions of Weakly Interacting Massive Particles (WIMPS). We have applied to this problem the technique of cryogenic detection and found for the two samples upper limits for contamination of 210 Pb of 4 and 7 mBq kg ˇ1 , the lowest ever determined for any type of lead. ” 1998 Published by Else

A calorimetric search on double beta decay of 130Te

We report on the final results of a series of experiments on double beta decay of 130 Te carried out with an array of twenty cryogenic detectors. The set-up is made with crystals of TeO2 with a total mass of 6.8 kg, the largest operating one for a cryogenic experiment. Four crystals are made with isotopically enriched materials: two in 128 Te and two others in 130 Te. The remaining ones are made with natural tellurium, which contains 31.7% and 33.8% 128 Te and 130 Te, respectively. The array was run under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. By recording the pulses of each detector in anticoincidence with the others a lower limit of 2.1 × 10 23 years has been obtained at the 90% C.L. on the lifetime for neutrinoless double beta decay of 130 Te. In terms of effective neutrino mass this leads to the most restrictive limit in direct experiments, after those obtained with Ge diodes. Limits on other lepton violating decays of 130 Te and on the neutrinoless double beta decay of 128 Te to the ground state of 128 Xe are also reported and discussed. An indication is presented for the two neutrino double beta decay of 130 Te. Some consequences of the present results in the interpretation of geochemical experiments are discussed. uf6d9 2003 Elsevier Science B.V. All rights reserved.

Challenges in Double Beta Decay

In the past ten years, neutrino oscillation experiments have provided the incontrovertible evidence that neutrinos mix and have finite masses. These results represent the strongest demonstration that the electroweak Standard Model is incomplete and that new Physics beyond it must exist. In this scenario, a unique role is played by the Neutrinoless Double Beta Decay searches which can probe lepton number conservation and investigate the Dirac/Majorana nature of the neutrinos and their absolute mass scale (hierarchy problem) with unprecedented sensitivity. Today Neutrinoless Double Beta Decay faces a new era where large-scale experiments with a sensitivity approaching the so-called degenerate-hierarchy region are nearly ready to start and where the challenge for the next future is the construction of detectors characterized by a tonne-scale size and an incredibly low background. A number of new proposed projects took up this challenge. These are based either on large expansions of the present experiments or on new ideas to improve the technical performance and/or reduce the background contributions. In this paper, a review of the most relevant ongoing experiments is given. The most relevant parameters contributing to the experimental sensitivity are discussed and a critical comparison of the future projects is proposed.

Physics potential and prospects for the CUORICINO and CUORE experiments

Abstract The Cryogenic Underground Observatory for Rare Events (CUORE) experiment projects to construct and operate an array of 1000 cryogenic thermal detectors of TeO 2 , of a mass of 760 g each, to investigate rare events physics, in particular, double beta decay and non-baryonic particle dark matter. A first step towards CUORE is CUORICINO, an array of 62 bolometers, currently being installed in the Gran Sasso Laboratory. In this paper we report the physics potential of both stages of the experiment regarding neutrinoless double beta decay of 130 Te, WIMP searches and solar axions.The CUORE experiment projects to construct and operate an array of 1000 cryogenic thermal detectors of TeO2, of a mass of 760 g each, to investigate rare events physics, in particular, double beta decay and non baryonic particle dark matter. A first step towards CUORE is CUORICINO, an array of 62 bolometers, currently being installed in the Gran Sasso Laboratory. In this paper we report the physics potential of both stages of the experiment regarding neutrinoless double beta decay of 130Te, WIMP searches and solar axions.

The thermal detection efficiency for recoils induced by low energy nuclear reactions, neutrinos or weakly interacting massive particles

Abstract We report the first direct measurements on the energy dependence of the thermal detection efficiency for heavy recoiling nuclei. Two bolometers made by TeO 2 crystals facing each other were operated at low temperature and read-out independently, while coincidence-anticoincidence techniques were used for particle discrimination. The experiment was carried out underground after implantation of both crystals with a source of 228 Ra. The relative response for alpha particles and nuclear recoils with respect to electrons of the same energy (Quenching Factor) was found to be compatible with or slightly larger than unity. Deviations from constancy with energy of the QF for nuclear recoils in α decays of 224 Ra, 220 Rn, 216 Po, 212 Po and 212 Bi were not observed.

The microcalorimeter arrays for a rhenium experiment (MARE): A next-generation calorimetric neutrino mass experiment

Abstract Neutrino oscillation experiments have proved that neutrinos are massive particles, but cannot determine their absolute mass scale. Therefore the neutrino mass is still an open question in elementary particle physics. An international collaboration is growing around the project of Microcalorimeter Arrays for a Rhenium Experiment (MARE) for directly measuring the neutrino mass with a sensitivity of about 0.2xa0eV/ c 2 . Many groups are joining their experiences and technical expertise in a common effort towards this challenging experiment. We discuss the different scenarios and the impact of MARE as a complement of KATRIN.

Vibrational and thermal noise reduction for cryogenic detectors

In this paper we present the excellent results obtained by mechanical decoupling of our thermal detectors from the cryostat. The starting point of this work is the necessity to improve the performances of thermal detectors and, besides, to eliminate the non-constant noise resulting from the overall cryogenic facility; this second point results to be crucial for rare-events experiments and the fundamental task for Dark Matter search. Tested on our bolometer, consisting of a 750 g tellurium oxide absorber coupled with an NTD thermistor and operated at &9 mK in an Oxford 200 dilution refrigerator, this powerful technique can, moreover, provide advantages for a large variety of thermal detectors. A good energy resolution of 3.9 keV FWHM was obtained for 2.615 MeV c-rays. The 4.2 keV average FWHM resolution for the 5407 keV 210Po a decay line is the best ever obtained for a-particles with any type of detector. ( 2000 Elsevier Science B.V. All rights reserved.